Mutation-testing mutators for Decimal calls.

Use all/0 to enable every Decimal-specific family alongside Mutare's built-ins:

# .mutare.exs
[mutators: [:builtins] ++ Mutare.Decimal.all()]

The families are:

• Mutare.Decimal.Arithmetic — same-arity arithmetic call swaps, reported as :decimal_arithmetic.
• Mutare.Decimal.Comparison — Decimal predicate/value comparison swaps and compare operand reversal, reported as :decimal_comparison.
• Mutare.Decimal.DefaultDrop — Decimal default/refinement argument drops, reported as :decimal_default_drop.
• Mutare.Decimal.LimitsDrop — Decimal parse/render limit argument drops, reported as :decimal_limits_drop.
• Mutare.Decimal.ModeSwap — Decimal rounding and string-format mode swaps, reported as :decimal_mode_swap.
• Mutare.Decimal.Classification — Decimal classification predicate swaps, reported as :decimal_classification.
• Mutare.Decimal.ZeroBoundary — Decimal sign predicates broadened around zero, reported as :decimal_zero_boundary.
• Mutare.Decimal.Transform — Decimal transform call removal, reported as :decimal_transform.
• Mutare.Decimal.Sign — Decimal sign-operation and constructor-sign swaps, reported as :decimal_sign.
• Mutare.Decimal.DivRem — Decimal.div_rem/2 tuple-order mutation, reported as :decimal_div_rem.
• Mutare.Decimal.Context — Decimal.Context call mutations, reported as :decimal_context.

The mutators match Decimal calls written qualified, aliased, imported, or as pipe stages.